The invention relates to gas turbines having guide and rotating blades that are cooled by cooling air in that the cooling air is guided through channels inside the blades. The invention relates in particular to a device for removing soil particles from the cooling stream, which prevents an obstruction of the channels in the blades.
When building gas turbines, the durability of the blades plays a significant role. Good cooling of the blades during operation is one of the measures that ensure durability. A known method of blade cooling is air cooling, in which air is guided from the compressor of the gas turbine into the turbine part while bypassing the combustion chambers. There, the cooling air flows through channels inside the blades, whereby it cools the blades, and then enters through outlet openings into the gas stream of the turbine. A frequently occurring problem in this type of air cooling is the obstruction of these channels with dirt particles that have reached the compressor from the ambient air or that have formed inside the machine and accumulate in the channels and outlet openings of the blades because of the cooling air.
U.S. Pat. No. 4,962,640 discloses a turbine guide blade that is hollow inside, whereby it has a second, internal wall with several small, laterally arranged openings in the hollow space. The cooling air flows from the radially outer end of the blade through an opening into the hollow space, and from there through small openings to the outer blade wall, whereupon it flows from the blade into the gas stream through additional openings. In order to avoid an obstruction of the small openings in the inside wall, the radially inside end of the blade has an opening that is several times larger than the former. At this larger opening there exists a greater drop in pressure than at the small openings in the side wall of the blade so that dirt particles in the cooling air pass through this larger opening and are removed from the cooling stream. The dirt particles enter through the larger opening into a space and then through a channel into the gas stream of the turbine.
U.S. Pat. Nos. 4,820,122 and 4,820,123 disclose two additional devices for removing dirt particles from the cooling air stream of a rotating blade. The rotating blades to be cooled are provided on the inside with labyrinth-like paths for the cooling air as well as a straight path for dirt particles which leads directly to an opening at the radially outer blade end. A deflection plate is provided at each entrance to the labyrinth-like cooling air paths. In order to reach the labyrinth-like cooling channels, the cooling air must greatly change its direction by flowing around the deflection plates. While clean cooling air or air with only very light particles is able to follow this change in direction, the heavier dirt particles are unable to follow this large change in direction because of their moment of inertia. Instead, they follow a less curved path and enter the straight duct that leads to the opening for the dirt particles.
In both of these devices, the dirt particles are separated from the cooling air stream because of an abrupt change in direction. This method of separation assumes that the cooling air stream has a relatively high speed.
This invention has the objective of providing a device and a process for removing dirt particles from the cooling air stream for a gas turbine blade in which the cooling air stream has a relatively low speed.
A gas turbine in accordance with this invention has guide blades and rotating blades that are attached to the housing of the turbine or the rotor. A supply line feeds cooling air through the turbine housing into the turbine. The rotating and guide blades each have cooling channels that pass through the inside of the blades. The cooling air flows through the cooling channels whereby it cools the blades, and then enters through outlet openings into the gas stream of the turbine.
The device for removing dirt particles in the cooling air stream is arranged according to the invention on a static part of the turbine and has a first and a second chamber, whereby a channel leads from the supply line for the cooling air to the first chamber. There is at least one conduit between the first and second chamber, whereby the direction of this conduit extends at an angle between 0xc2x0 and 90xc2x0 to the rotor axis, whereby an angle of 0xc2x0 corresponds to a parallel to the rotor axis, and an angle of 90xc2x0 corresponds to a parallel to the tangent to the rotor circumference. There is also a drop in pressure from the first to the second chamber of the device, so that the cooling air is accelerated on the way from the first to the second chamber, whereby it receives a speed component in the circumferential direction of the rotor. The second chamber has two rows of outlet openings that are arranged on different radii in relation to the rotor. The first row of outlet openings is arranged radially further inside in reference to the conduit between the first to the second chamber and leads to the inlet of the cooling channels of the guide or rotating blades. The second row of outlet openings is arranged radially further outside in reference to the conduit between the first and the second chambers and feeds cooling air in the direction of the gas stream of the gas turbine.
According to the method of the invention, the cooling air is collected in the first chamber of the device according to the invention and is accelerated by a first drop in pressure from the first to the second chamber, whereby the cooling air receives a speed component in the direction of the rotor circumference. In the second chamber, dirt particles contained in the cooling air are removed by centrifugal force in that particles enter through the radially outer outlet openings from the second chamber and flow into the gas stream, and the cleaned cooling air flows through the radially inner outlet openings from the second chamber to the inlet of the cooling channels of rotating or guide blades.
The first chamber of the device according to the invention is used to collect the cooling air from the compressor in a static part of the turbine at a given pressure. The cooling air flows through the single or several conduits to the second chamber and is hereby accelerated by the drop in pressure between the two chambers, whereby it receives a speed component tangentially to the rotor circumference because of the orientation of the conduit.
The second chamber is used to separate the dirt particles from the cooling air stream by means of centrifugal force. The cooling air there flows in part tangentially to the circumference of the rotor. This tangential acceleration causes the cooling air to receive a radially outward directed speed component, so that the heavier dirt particles are driven radially outward, and the lighter and clean cooling air flows on a radially inner path. The rows of outlet openings on two different radii are used for the exit of the clean cooling air to the guide or rotating blades or the exit of the dirt particles into the gas stream. This means that the clean cooling air reaches the cooling channels of guide or rotating blades separately from the dirt particles, while the dirt particles are driven directly into the gas stream and do not reach the cooling channels.
In a first variation of the invention, the device for removing dirt particles is arranged at an inside housing part of the turbine. The first and second chambers of the device hereby each extend over the entire circumference of the turbine.
In a second variation of the invention, the device is again arranged at an inside housing part, whereby the first and second chamber each consists of several partial chambers. These partial chambers each extend over a part of the housing circumference, whereby they cover the entire circumference of the housing together.
In a third variation, the device is arranged at the radially inner end of guide blades of the turbine. First and second chambers hereby each extend over a part of the circumference of the guide blade row, for example, over four guide blades. In this case, the device again consists of several first and several second chambers or partial chambers that together cover the entire circumference of the guide blade row.
In a preferred embodiment of the invention, the number of radially inner outlet openings in the second chamber is greater than the number of radially outer outlet openings. The diameter of the radially inner outlet openings is hereby smaller than the diameter of the radially outer outlet openings, whereby the latter is at least equal to the diameter of the dirt particles to be removed. The radially outer outlet openings are not only used for the exit of dirt particles, but also the exit of a cooling air stream that flows from the radially inner parts of the turbine to the gas stream and counteracts the entrance of hot gases into the cooling channels of the rotating blades.
In another embodiment of the invention, the wall in the second chamber that is located opposite from the conduits between the two chambers is angled in the direction of the cooling air stream and radially outward. This facilitates the movement of the dirt particles in radial direction to the radially outer outlet openings.
In another embodiment, the wall in the first chamber located opposite from the conduits to the second chamber is angled in the direction of the conduits to the second chamber, so that the cooling air stream flowing into the first chamber is deflected in the direction of the conduits to the second chamber.
In yet another embodiment, there is a drop in pressure above the outlet openings for the clean cooling air from the second chamber. Because of this, the exiting clean cooling air stream is accelerated during its exit in the direction of the rotor rotation, which contributes to the optimization of the turbine power.
In another embodiment, these outlet openings are directed radially outward at an angle in relation to the flow direction within the second chamber, so that the clean cooling air stream is better able to reach the inlet to the cooling channels of the rotating blade.